Method of and system for monitoring and diagnosing a grounding system, use of rotating electrostatic motor to diagnosing

ABSTRACT

The disclosure includes a method of diagnosing a grounding system of a structure that includes a charge collecting structure conductively connected to the ground via a grounding path, where diagnosing involves an act of monitoring output of a voltage and/or a current and/or an electrostatic detector connected to the grounding path.

FIELD OF THE DISCLOSURE

Disclosed is a system and a method of diagnosing a grounding system of astructure comprising a charge collecting structure conductivelyconnected to the ground via a grounding path, wherein diagnosinginvolves an act of monitoring output of a voltage and/or current and/orelectrostatic detector connected to the grounding path.

BACKGROUND

Structures erected or operated under ambient conditions often experienceelectrical charges and electrostatic fields. Structural elements collectelectrostatic charge. In example towers, tall buildings, bridges,spheres (like Horton spheres) used for storing compressed combustiblegases, street lights, etc. may be such structures, objects which canproduce — not only collect — electrostatic energy constantly, partially,periodically.

Such structures are subjected to harsh weather conditions, includinglightning. Technical means, systems, and methods exist to mitigate theeffect of lightning for example on a wind turbine generator. Groundingor earthing arrangements of different types exist to protect suchstructures from damage and will increase their lifetime.

However, unintentional fully or partly disconnection of the groundingsystem, wear and tear, lightning, and general discharging alter thegrounding systems and grounding systems must receive periodic inspectionand maintenance throughout the life to retain its effectiveness. Thereis a need for monitoring, diagnosing and providing information about theactual conditions or workings of grounding or earthing systems.

The electrostatic energy associated with the induced charge on theerected structures represents an ambient energy source. For example,lightning strikes can provide power in the range of GW. Conventionalgrounding systems transfer this induced static charge to earth,resulting in the energy associated with static charge not being utilizedat all. The ability to harvest and store, at least a small percentage ofthis ambient energy, otherwise dissipated through the grounding systems,will provide manageable energy reserves. The erected structures use awide array of sensors as part of monitoring systems, including thegrounding monitoring system.

An exemplary structure may be a wind turbine generator.

Lightning is an electrical discharge within clouds, from cloud to cloud,or from cloud to the earth. It is known in the industry that the mostsignificant danger facing wind turbines is damage from lightningstrikes. A German study found that 80% of wind turbine insurance claimspaying out for damage compensation were caused by lightning strikes. 85%of the downtime experienced by one commercial wind farm in the USA wasfound to be related to lightning strikes, costing around USD250,000 inthe first year of operation alone. And as another example, a large windfarm in the North Sea, near the German island of Helgoland, sufferedlosses because of lightning strikes so large that its operation was nolonger cost effective. Lightning faults cause more loss in wind turbineavailability and production than the average fault. The number offailures due to lightning strikes is known to increase with tower heightand a growing number of studies speculate that rotating wind turbinesmay be more susceptible to lightning strikes than stationary structures.Given that turbine heights are expected to increase, and the renewableenergy industry is growing, the number of failures is likely to growwith them.

To reduce the likelihood of lightning damage, lightning protectionsystems are built into the wind turbine structures to safeguard againstdamage or injury caused by lightning or by currents induced in the earthfrom lightning.

The major purpose of built-in grounding systems is to conduct the highcurrent lightning discharges safely into the earth. A well-designedgrounding system will minimize voltage differences between areas of astructure and offer protection against damage.

These built in grounding systems offer protection against both directand indirect effects of lightning. The direct effects are burning,blasting, fires and electrocution. The indirect effects are deficientoperation of control or other electronic equipment due to electricaltransients.

The grounding system takes the form of a low resistance path to ground.The path goes from the blade’s tip to the base of the turbine. In theevent of a lightning strike, current will flow to ground through thelightning protection system, not the sensitive equipment in the windturbine. To ensure that the protection will work when needed, theresistance of the path to ground is checked and measured at regularintervals, making sure it meets the limits specified by the turbinemanufacturer (typically limited to 15-30 mΩ, depending on turbine size).

However, the blades flexes with the wind and are under strain etc., andtherefore wear and tear, lightning, general discharging and intentionalor unintentional fully or partly disconnection of the grounding systemalter the grounding systems. The industry practice today is thatgrounding systems therefore receive periodic inspection and maintenancethroughout its lifespan to retain its effectiveness. Since the periodicinspection clearly is not sufficient to secure a permanent efficientgrounding or earthing system, it will be advantageous to monitor,diagnose and provide information about the actual conditions or workingsof grounding or earthing systems.

Known art comprises some relevant disclosures including the following,where IOP Publishing under Smart Materials and Structures 24 (2015)033001 presents a topical review of “A review of damage detection methodfor wind turbine blades” by Dongsheng Li et al. Furthermore, moredetailed aspects are disclosed in e.g. the patent literature, whereGB2463818A discloses a device detecting lightning currents in a windturbine, JP2017020423A discloses an external lightning protection systemfor wind turbine blades, and US2013336786A1 discloses aspects of asystem and method for automatically inspecting a lighting protectionsystem on a wind turbine generator.

SUMMARY

It is an objective to improve monitoring the discharging ofelectrostatic electricity and events, such as lightning strikes and theefficiency of the grounding system, and provide relevant informationwhen there is a need for inspection or improved correct grounding orearthing of erected structures, including those of wind turbinegenerators.

An object is achieved by a method of diagnosing a grounding system of astructure comprising a charge collecting structure conductivelyconnected to the ground via a grounding path, wherein diagnosinginvolves an act of monitoring an output of an electrostatic motorconnected to the grounding path.

As will be disclosed, diagnosing or monitoring of the efficiency of thegrounding system of a structure may be performed by means of monitoringthe efficiency of an electrostatic motor. This may be done incombination with a generator driven by the torque from the electrostaticmotor. These devices can not only monitor whether or not the groundingsystem is connected, they can also monitor the quality/efficiency of thegrounding system. Monitoring of the efficiency of the devices canfurthermore be used to quantify or detect the event of a lightningstrike hitting the structure. Moreover, one or more of the presentedembodiments in combination can also be used to monitor the passage ofcurrent, which for example is critical for the lifetime of specificcomponents installed in a structure, such as a wind turbine generator,and can in example diagnose if the neutral brush is not fully connectedor damaged or worn off.

Part of this invention is related to harvesting from energy reservesfrom the ambient electrostatic energy which for example can be utilizedto power monitoring systems. This ensures that monitoring systems areself-sufficient, self-contained and capable of operating without humanintervention for a long period. This can reduce maintenance costs andprovide economic benefits.

In an aspect, the output of the electrostatic motor is a function ofcollected charge conducted to the ground. The output may be a functionof relative measures.

Such measures may include a measure of rotational speed of theelectrostatic motor. The rotational speed is a very simple and robustindication. The rotational speed is easy to monitor and to communicate.The rotational speed may be a relative measure compared to a calibrationvalue or simply a relative value compared to a reference value.

Such measure may be a measure of the torque of the electrostatic motor.The torque is easy to monitor and to communicate. The torque may be arelative measure compared to a calibration value or simply a relativevalue compared to a reference value.

A person skilled in the art will appreciate combining measuredcombinations thereof.

Measure may be relative to a respective calibrated measure performedagainst measure form a standard such as a grounding standard orprocedure.

Standard IEC 61400-24 for lightning protection of wind turbines may beused as a reference. Standard IEC 61662 for lightning risk to astructure may be used. Standard IEC 61024-1 for lightning protectionstandard (earthing/grounding) may be used. Standard IEC 62305 forgeneral standard may be used

The measures or indications may be converted and transmitted by atransmitter connected to the system.

As an example, wind turbine structure’s sensors can be installed in anyplace where there is a grounding path or earth cable (blade, hubcabinet, nacelle, azimuth level, sections, ground cabinet, etc.).

The measures or indicators may be quantitative, say “Good grounding: Ifthe receiver doesn’t detect voltage” the charge or current goes to theground and is eliminated. “Faulty grounding: Signal will not beeliminated to the ground”, a measurement is detected and a signal issent as an alarm/warning message.

The measurements may be from the electrostatic motor and based on therotational speed (in RPM) of the shaft or the torque on the shaft. Themeasurement may be of a voltage of a generator, driven by the torquefrom the electrostatic motor. Such measurement may be used to monitorand quantify the efficiency of the grounding system in a post processingof these collected data.

An indicator could also be “Insufficient grounding,” in case thegrounding connection is unstable or lost completely.

In an aspect there may be a further act of generating power by generatormeans driven by the torque on the axel or shaft from the electrostaticmotor.

Thereby, it can be achieved that power can be generated at location andcan reduce or eliminate the need for further power supply.

As an example, the following configuration can be used as a startingpoint for a system in a wind turbine generator. The electrostatic motormay be say a 24 VDC motor. The motor may operate with a rotational speedin a range of 0-420 RPM and generate a torque of about 0.5 Nm.

Such motor may drive a generator operating in say 0-2100 RPM andgenerate about 3 W as 6 V.

A person skilled in the art will easily find required elements asoff-the-shelf elements and make the required adjustments.

For a wind turbine generator, an exemplary setup has a generator outputof 1-6.5 V AC which may also be used as a measure. This output voltageAC can be converted to usable DC voltage to power the devices by meansof a simple Power management circuit.

A gear may be inserted between the electrostatic motor and thegenerator.

In an aspect the monitoring of the grounding is powered by the powergenerated by the electrostatic motor. As such the monitoring may be asingle standalone unit that can operate in or close to the structure.

In a wind turbine generator the monitoring may be performed say in ablade and the result of the monitoring may be transmitted wirelessly.

In an aspect, the acts outlined in diagnosing the grounding system is ofa lightning protection system and the structure comprises parts of awind turbine generator.

In an aspect, the structure comprises a blade, which may be a rotorblade of a wind turbine, and the act of monitoring includes an act ofdetecting a lightning strike. There may be an act of detectingelectrostatic discharge. There may be combinations thereof.

In an aspect, the acts outlined in diagnosing the grounding system is ofa lightning protection system and the structure comprises parts of abuilding, a bridge, or storage tanks of combustible fuels/gasses.

A person skilled in the art will be able to construct a groundingdiagnostic system based on an electrostatic motor and means adapted toexecute or perform the acts outlined.

A grounding diagnostic system may be configured to diagnose a groundingsystem of a structure and comprise a charge collecting structure that isconductively connected to ground. The connection to ground may be via agrounding path. Such grounding path may be by design and includespecific conductors or connections that define a preferred path. Agrounding path may also be inherent according to a design and be thepath with the least resistance. A grounding path may also be a result ofa fault, wear and tear or emerging short circuits.

A person skilled in the art and say operating wind turbine generatorswill appreciate that the correct path of the electrostatic energydischarge should be according to an installed lightning groundingsystem. This means from the collectors in the blades bypassing the bladebearings and through the hub and again passed the bearings of therotating part of the drive train by neutral brushes to the groundingsystem.

As an example, if the neutral brushes are not well connected or damaged,there is a risk that the electrostatic energy, and lightning, willfollow a path through the main shaft bearings and small sparks duringdischarge will damage the bearing balls or even worse through thegearbox or generator.

The grounding system may comprise an electrostatic motor configured tobe connected to a connection path of the grounding system.

There may be a monitoring unit configured for monitoring an output ofthe electrostatic motor and/or monitoring the output of a generatorconnected to the electrostatic motor. The output may be as a function ofcollected charge, electrostatic potential, or charge conducted toground.

The output may be rotational speed, torque or alike, as outlinedpreviously. Such output is simple and robust and yet indicative.

In an aspect, the electrostatic motor is configured with powergenerating means to generate power. The power generating means may be agenerator or dynamo of a size according to the circumstances. For a windturbine generator the specifications may be as outlined.

In an aspect, the electrostatic motor is configured with powergenerating means to generate power and storage elements to store thepower. The power generating means may be a generator or dynamo of a sizeaccording to the circumstances. The storage element can for example be abattery or supercapacitor or flywheel of a size according tocircumstances. For a wind turbine generator the specifications may be asoutlined.

In an aspect, the grounding diagnostic system is further configured withthe power generating means powering the grounding diagnostics systemsalone.

There may further be energy storage systems operating in connection withthe power generating means. Such energy storage systems and powergenerating means (e.g. a dynamo) may include a power management system.

The harvested power or energy may be used for powering for example asensor node, and may also be used for powering other electricityconsuming devices.

The above disclosed may be used as a framework for wind turbinegenerators or any erected structure along with the electrostatic motorand storage system as an ambient static charge energy harvester Thisenergy can be utilized to power the grounding diagnostic systems or evenan entire monitoring system making such systems self-reliant andself-contained.

Thereby, the system can be placed on one or more locations of thestructure being diagnosed. Signals may be generated and transmitted anddiagnosis can be performed at all times and with flexibility. Adiagnostics system may comprise a unit in multiple wind turbine bladeswhich each transmits measured output wirelessly to one or more centralmonitoring units. In such an installation, the grounding of respectiveblades can be monitored and relative differences can easily be detected.Units may be placed at other locations and ease or enable relevantreferences with fault detection and localization.

The measured or monitored values may also be related to predestinedvalues from other structures. As an example, a diagnostics system may beinstalled on multiple wind turbine generators and measurements from onewind turbine generator may be compared to measurements from one or moreother wind turbines.

A person skilled in the art will appreciate the aspect where a computerprogram product is established that comprises instructions to cause thegrounding diagnostic system to perform the acts involved in diagnosing.

The above diagnosing can be performed or the diagnosing system can beconfigured with reference values according to specifications such asstandards or operating procedures related to a structure e.g. a windturbine generator.

The diagnostics may be done by monitoring measurements from two bladeson the same wind turbine generator that experience exactly the sameenvironmental conditions at the same time.

The diagnostics may be done by monitoring measurements from multiplewind turbine generators in a farm that experience exactly the sameenvironmental conditions at the same time.

In an aspect, there is a method of diagnosing a grounding system of astructure comprising a charge collecting structure conductivelyconnected to ground via a grounding path and wherein diagnosing involvesan act of monitoring outputs of a voltage detector connected to thegrounding path.

A voltage detector can be used or a device indicating the passage ofvoltage or electrostatic discharge in a cable.

As an example, a Rogowski coil, a current sensor or any similar device,which measures the passage of charges, may be used.

As an example, the voltage detector is a contactless voltage detectordevice blinking periodically according the voltage levels. Such detectormay be a voltage detector for a bus bar, which device is suitable forthe continuous indication of voltage being present on bus bars and otherequipment: Off-the-shelf detectors may operate a nominal voltage of10-36 kV.

In an aspect, diagnosing involves an act of comparing outputs of atleast two voltage detectors connected at two different points of thegrounding path.

As an example, monitoring the status of the neutral brush on a windturbine generator may be possible using measurements from two voltagedetectors. If the neutral brush is healthy and working as intended, thevoltage detector one will measure the whole or the highest amount ofenergy during the discharging in comparison to voltage detector two,which is measuring the voltage on the nearest grounding cable.

If voltage detector two measures most of the energy or higher than thedefault, the system knows that the neutral brush is not providing themost efficient connection to the grounding system — and grounding hasfound an alternative route.

According to the neutral brush or grounding system complexity, multiplevoltage detectors can be installed to check the right path of thedischarging energy as needed.

In an aspect, there is a grounding diagnostic system having two voltagedetectors and means adapted to execute the acts as described.

In an aspect, of diagnosing a grounding system of a structure,diagnosing is performed as a function of measures based on one or moreelectrostatic motors and one or more voltage detectors as outlined.

In an aspect, there is a grounding diagnostic system having anelectrostatic motor and means adapted to execute the acts outlined andhaving one or more voltage detectors and means adapted to execute theacts as outlined.

In general, a method is disclosed of determining grounding of agrounding system of a wind turbine generator. The method comprises actsthat involve building up electric charge in a capacitor, say bycollecting electrostatic charge from at least one wind turbine blade.

There is an act of discharging the capacitor at a discharge charge levelor discharge voltage at a point on the wind turbine blade. There is anact of measuring a grounding charge level or grounding voltage at agrounding system point of the wind turbine. There is an act ofdetermining grounding of the grounding system as a function of thedischarge charge level or discharge voltage and the grounding chargelevel or grounding voltage.

The grounding system point may be located in the nacelle, in the tower,or blade of the wind turbine generator (WTG).

As outlined above, a rotating electrostatic generator or motor may beimplemented as disclosed. Such implementation provides for additionaldiagnostics or methods of diagnosing. In relation to wind turbinegenerators, several usages of a rotating electrostatic motor may applyfor such diagnostics or methods of diagnosing.

There may be a use of a rotating electrostatic motor arranged in a windturbine generator to diagnosing an operational condition of the windturbine generator. There may be a method of diagnosing operationalconditions of a wind turbine generator, which is performed by use of arotating electrostatic motor arranged in a wind turbine generator.

In an aspect, diagnosing is of degeneration in the wind turbine bladesof the wind turbine generator (WGT). There may be a method of diagnosingdegeneration of a wind turbine generator by use of a rotatingelectrostatic motor.

Thus, the electrostatic motor can be used to detect the degradation inthe wind turbine blades. The blade degradation or corrosion may be ofthe type of leading-edge erosion that may occur in the long-termoperation wind turbine. Other types of more event-like types ofdegeneration may be sudden damages that occur and can be observed as“steps” in the diagnostic output. As an example, an increase of thesurface roughness of the blades will ultimately lead to higher staticcharge formation, and thus the surface roughness can be found,reversibly.

In an aspect, the diagnosing is performed by comparing a diagnosticoutput from a rotating electrostatic motor coupled to one blade with adiagnostic output from another rotating electrostatic motor coupled toanother blade on the same wind turbine generator.

In an aspect, the diagnosing is performed by comparing a diagnosticoutput from a rotating electrostatic motor coupled to one blade with adiagnostic output from another rotating electrostatic motor coupled to asimilar blade of another wind turbine generator.

In an aspect, the diagnosing is performed by comparing a diagnosticoutput from a rotating electrostatic motor coupled to one blade with areference value. The reference value may be from the group of blades ofthe blade type. The reference value may be of historical data from theactual blade itself.

In an aspect, data may be collected in the same time slot from one ormore other blades on this specific wind turbine generator Alternatively,data may be collected in the same time slot from one or more otherblades from other wind turbines in the same wind farm.

Using the above disclosed implementations, a change such as an increasein static charge can be identified through monitoring the speed andbehavior of the electrostatic motor. To distinguish this from the poorgrounding scenario outlined, minor modifications are required, which canbe by characterizing the motor behavior under for example, leading edgeerosion of a blade. In an implementation, the diagnostic may be used todefine a machine learning algorithm which can self-identify thesecharacteristics. The algorithms can make decisions or diagnosis by oneor more of the following. By comparing measured output fromelectrostatic motor with that of the motors in other blades of sameturbine. By comparing measured output from electrostatic motor with thatof the motors in other blades of turbines of same type in same farm. Bycomparing the output of the motor to a reference value.

In an aspect, the diagnosing is of a grounding system of the windturbine generator as outlined above.

In an aspect, the diagnosing is of a wind speed under which the windturbine generator is operating. There may be a method of determiningwind speed experienced by a wind turbine generator, the method comprisesuse of a rotating electrostatic motor.

The static charge generated on the blades is dependent on the windspeed, thus reversely the diagnostic output of the rotatingelectrostatic motor may determine the windspeed. The higher the windspeed, the higher the charge. Therefore, by monitoring the output of theelectrostatic motor, correlating with other factors like temperature,atmospheric pressure etc. and using a suitable computer algorithm,calculation of wind speed can be achieved. This may be furtheradvantageous and significant as it allows to achieve higher accuraciesin wind speed measurements than using anemometer placed at the backsideof a wind turbine since their measurements are affected by the wakeeffect. The measurement of wind speed can for example be used in theimproving of the control of a wind turbine.

A further use of a rotating electrostatic motor may be to kick start orgive a start torque to get the motor operational. Such kick starting maybe done using the generator which is coupled to the rotatingelectrostatic motor for power generation. By momentarily running thegenerator as a motor at the beginning of the operation, the necessarystarting torque for the electrostatic motor can be provided. It may bean advantage for the generator to be connected in such a way that thestarting torque is in the direction to ensure sustained operation of themotor.

Another way to initiate the starting torque or kick starting, may be byusing the centrifugal forces acting on the motor as a result of therotating blade. Through this, the need for an external provider forstarting torque can be eliminated. In this case, the motor should beplaced in the blade such that the centrifugal forces exert the startingtorque in the direction so that the motor can sustain the operation.

A further use of a rotating electrostatic motor may be the diagnosing ofa lightning strike of the wind turbine generator. There may also be ause of a rotating electrostatic motor where diagnosing is performeddiscriminating between a lightning event and electric chargeaccumulation. The outlined output from the rotating electrostatic motor,e.g. voltage, torque etc., has shown to comprise distinctivecharacteristics that can be associated with respective lightning andelectrostatic charge.

The use of the rotating electrostatic motor may be such that thediagnosing of lightning includes accessing characteristics of the outputfrom the rotational electrostatic generator at either the wave front,wave tail, or both.

Thus, the rotating electrostatic rotor implemented in a wind turbinegenerator as disclosed can be used to quantify the characteristics of alightning, e.g. lightning current. Realizing this use, then whenlightning strike, the motor will accelerate, and the speed profile ofthe motor tend to follow the waveform of the lightning strike. Thus,using a suitable computer algorithm, and using the historical speedbehavior, the wave shape can be reconstructed i.e. the wave front andtail. Along with this, using the absolute speed value of the motor, thecharge associated with the strike can be estimated. As outlined above,this can be used to differentiate between a lightning event andelectrostatic charge accumulation under normal operation. Measuring andaccounting for other parameters like measured wind speed, humidity canalso be used to characterize or diagnose events. Such analysis may beimplemented in the computer algorithm.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be described in the figures, whereon:

FIG. 1 illustrates a structure with a charge collecting structure and agrounding path, according to an example.

FIG. 2 illustrates a wind turbine generator structure with a groundingdiagnostics system where the voltage detectors are used with sensornodes, according to an example.

FIG. 3 illustrates a wind turbine generator with grounding paths,according to an example.

FIG. 4 illustrates a rotor and nacelle system with sensors fordiagnosing grounding, according to an example.

FIG. 5 illustrates a wind turbine generator with a grounding system in anacelle - with grounding along a grounding path, according to anexample.

FIG. 6 illustrates a wind turbine generator with a grounding system in anacelle - with grounding along an in-correct grounding path, accordingto an example.

FIG. 7 illustrates a configuration of ground diagnosing using anelectrostatic motor and with electrostatic energy harvesting, accordingto an example.

FIG. 8 illustrates a configuration of direct ground diagnosing usingelectrostatic motor, according to an example.

FIG. 9 illustrates a configuration of direct grounding diagnostics usingvoltage and/or current and/or electrostatic detector, according to anexample.

FIG. 10 illustrates a configuration of grounding diagnostics usingvoltage and/or current and/or electrostatic detector and energyharvesting, according to an example.

FIG. 11 illustrates a method of diagnosing a grounding system of astructure, according to an example.

DETAILED DESCRIPTION

Item No Structure 1 Wind Turbine Generator (WTG) 12 Tower 13 Rotor 14Nacelle 19 Blade 22, e.g. 22A, 22B, 22C WTG generator 28 WTG gearbox 30Sensor node 45, 45A, 45B, 45C Collection cabinet 50 Communication module54 Grounding system / Grounding diagnostic system 100 Lightningprotection system 102 Charge collecting structure 120 Grounding path 122Grounding path point 124I, 124II Grounding path critical transition 126In-correct grounding path 128 Voltage and/or current and/orelectrostatic detector 130, 130I, 130II Electrostatic motor 140 Output142, 142I, 142II Generator means 150 Generator 152 Power managementcircuit 154 Energy storage 156 Gearbox 160 Power transmission 170 Otherpower consuming installations 180 Ground 190 Lightning strike 192Electrostatic discharge 194 Method of diagnosing 1000 Monitoring 1100Generating 1200 Detecting 1300 Comparing 1400

FIG. 1 illustrates a structure 1 with a charge collecting structure 120and a grounding path 122.

The ambient atmosphere to the structure 1 can create charge by lightningstrike 192 or static charge 194 by interaction between the atmosphereand the structure 1 due to a relative movement between the atmosphereand the structure 1.

The relative movement can be due to wind or wind and sand or due to thestructure 1 having one or more moving parts.

The structure 1 has the charge collecting structure 120 with a groundingpath 122, wherein the grounding path 122 is designed for the structure 1such that the structure 1 is controllably grounded. The grounding path122 is connected to the ground 190.

The charge may arise from electrostatic discharge 194 or from lightning192.

However, the grounding may happen by one or more in-correct or missinggrounding paths 128, which causes a current to travel along thein-correct grounding paths 128. This may cause damage to equipment ormay uncontrollably generate sparks, which in worst case may cause afire.

The in-correct grounding path 128 may happen anywhere along thegrounding path 122 due to fatigue or errors in equipment. However, anystructure 1 will typically have one or more grounding path criticaltransitions 126, wherein the risk of having an incorrect grounding path128 is higher.

A grounding path critical transition 126 can be a transition between arotational element and a stationary element.

In FIG. 1 the grounding path 122 has two grounding path criticaltransitions 126 and two associated in-correct grounding paths 128.

The structure 1 is equipped with a sensor node 45 for monitoringgrounding path 122 at a grounding path point 124 which is at one of thegrounding path critical transitions 126; thereby, the sensor node 45 candetermine whether the charge is grounded via the intended grounding path122.

The sensor node 45 may be part of a not shown grounding diagnosticssystem 100.

FIG. 2 illustrates a wind turbine generator (WTG) 12 structure 1, with agrounding diagnostics system 100.

The WTG 12 is a structure 1, wherein grounding due to charge generationis needed.

The WTG 12 comprises a tower 13, a nacelle 19 with a WTG generator 28and WTG gearbox 30 connected via a rotor 14 to blades 22A, 22B and 22C.

The structure 1 has a grounding path 122 illustrated with the black andsolid line. The figure discloses two possible in-correct grounding paths128 through the WTG generator 28 and the WTG gearbox 30, which may causedamage to the respective equipment.

Although not specifically disclosed, the blades 22A, 22B, 22C, where themain part of the charge is generated due to collision with the ambientatmosphere, are susceptible to have in-correct grounding paths 128. Thismay happen due to wear on neutral brushes which wear out over time dueto friction from turbine operation. This, however, needs periodicmaintenance and replacement if necessary, and, related to this, correctspare parts can be installed or serviced incorrectly, or incorrect spareparts not feasible for the specific application can be used.

Thus, each of the blades 22A, 22B, 22C are equipped with a sensor node45A, 45B, 45C configured for at least monitoring whether thecorresponding blades 22A, 22B, 22C are grounded along the intendedgrounding path 122.

The structure 1 also has a sensor node 45, voltage and/or current and/orelectrostatic detector 130 at the interface between rotor 14 and nacelle19.

The structure 1 also has a sensor node 45, voltage and/or current and/orelectrostatic detector 130 at the interface between the tower 13 andnacelle 19.

The nacelle 19 is equipped with a collection cabinet 50 being incommunication with the different sensor nodes 45, 45A, 45B, 45C via anot shown communication module 54. The collection cabinet 50 and thesensor nodes 45, 45A, 45B, 45C form part of the grounding diagnosticsystem 100.

Thereby, the grounding diagnostic system 100 will be able to at leastmonitor the grounding path 122 such that if a change is monitored atblade 22A, there will likely be an in-correct grounding path 128 in theblade 22A.

Thus, when electrostatic electricity (or lightning) is generated in theblades 22, it is being discharged correctly from the blades 22. Theelectrostatic electricity (or lightning) does NOT pass through bearings(WTG gearbox 30 and or WTG generator 28 etc.) — but the electrostaticelectricity (or lightning) must avoid the bearings (WTG gearbox 30 andor WTG generator 28 etc.) by following the grounding system 100 beingdesigned with the grounding path 122.

FIG. 3 illustrates a wind turbine generator 12 with grounding paths.

The wind turbine generator (WTG) 12 is a structure 1. The WTG 12comprises a tower 13, a nacelle 19 with a WTG generator 28 and WTGgearbox 30 connected via a rotor 14 to blades 22.

The WTG 12 is connected to the ground 190.

The figure discloses grounding path critical transitions 126 for the WTG12. The grounding path critical transitions 126 are at transitionsbetween moving parts of the WTG 12, and at the WTG generator 28 and theWTG gearbox 30 connection with the nacelle 19, because it is importantthat the WTG 12 is not grounded through said parts.

Thus, when electrostatic electricity (or lightning) generated in theblades 22 is being discharged correctly from the blades 22, theelectrostatic electricity (or lightning) does NOT pass through bearings(WTG gearbox 30 and or WTG generator 28 etc.) — but the electrostaticelectricity (or lightning) must avoid the bearings (WTG gearbox 30 andor WTG generator 28 etc.) by following the grounding system 100 beingdesigned with the grounding path 122.

FIG. 4 illustrates a rotor 14 and nacelle 19 system with sensors 45 fordiagnosing grounding.

The WTG 12, structure 1 is equipped with a charge collecting structure120, wherein blades 22A, 22B and the nacelle 19 are connected to theground 190 through the tower 13. The grounding path 122 from blades 22to the ground 190 is shown with bold arrows.

The transitions between the blades 22A, 22B and the rotor 14 aregrounding path critical transitions 126 wherein neutral brushes aredesigned to ensure the correct grounding path 122. However, the neutralbrushes experience high amounts of wear and tear and are thus prone tobreakage or drop in function over time.

This will cause the grounding to find an alternative route, which worstcase is through the bearings. Such an alternative route is denoted anin-correct grounding path 128.

The blades 22 will experience electrostatic discharge 194 due tobuild-up of charge. The blades 22 are grounded by the grounding path122.

The WTG 12 structure 1 is equipped with a grounding diagnostic system100 monitoring whether the WTG 12 structure 1 is grounded along thegrounding path 122 or whether the system is grounded along an in-correctgrounding path 128 (not shown in FIG. 4 ).

The grounding diagnostic system 100 comprises different types ofsensors, depending on whether the sensor node 45 is placed in the blade22 or in the nacelle 19.

Each blade 22 is equipped with an electrostatic motor 140, which ispowered by the electrostatic charge. The electrostatic motor 140 has anoutput 142 (not shown), which can at least be quantified such that asensor 45 can monitor the grounding path 122.

However, the output 142 of the electrostatic motor 140 can be used topower the sensor monitoring the grounding path 122. In some embodiments,the electrostatic motor 140 may even power other sensors not related tothe grounding diagnostic system or be used to power a low powerconsuming de-icing system.

The sensor node 45 may monitor the efficiency of the electrostatic motor140 and thereby be able to determine whether the grounding is along thegrounding path 122.

As an example, if the sensor node 45 measures a sudden drop inefficiency or power generated, it will likely be due to the groundingbeing along an in-correct grounding path. This may be caused by breakageor damage of one or more of the neutral brushes in the blade 22 suchthat the grounding is along an in-correct grounding path 128.

Examples of the sensor node 45 and electrostatic motor 140 are disclosedin FIGS. 7 and 8 .

The two sensor nodes 45 in the nacelle 19 may monitor output from avoltage detector 130 or a current detector in combination with an outputfrom an electrostatic motor 140. The sensor node 45 may performmonitoring and comparing of two or more sensory outputs.

The sensor node 45 include sensory output from the electrostatic motor140 and the sensory output may be handled by the sensor node 45, whichmay be independent of the voltage detector 130 or a current sensor. Thesensor node 45 may comprise an accelerometer, temperature sensor or anyother sensor. The sensor node 45 may include a processor(microcontroller/microprocessor) or any processing unit where allcomputational logic may be implemented. By taking the inputs fromelectrostatic motor 140 or voltage detector 130/current sensor or anysimilar sensor to detect the passage of charges, this can process themeasured values/information and transmit an alarm or signal via thecommunication module if necessary, e.g. to a collection cabinet 50 innacelle 19.

The sensor node 45 communicates with the collection cabinet 50 which isalso equipped with a communication module 54.

The voltage detector 130 may be self-powered, wherein a light emitter isadjusted to blink as a function of the voltage level. The voltage levelis a direct measurement of the efficiency of the grounding cable. Thisis disclosed in greater detail in FIG. 9 .

The sensor nodes 45 communicate through a collection cabinet 50 eitherwireless or by wire. The sensors 45 in the blades 22 will typicallycommunicate wireless such as via radio-frequency.

The collection cabinet 50 may have means for performing a method ofdiagnosing or have means to communicate through a central server fromwhere the method of diagnosing can be performed.

The processing of data can in principle be done locally in the sensornode 45. The processing may be performed locally in between more thanone sensor nodes 45. The processing may be performed in the datacollection box in the structure, e.g. in a wind turbine generator. Theprocessing may be performed in a central server where data istransferred to and processed.

The correct path of the electrostatic energy discharge is according tothe arrows on the first slides (following the installed lightninggrounding system): this means from the collectors in the bladesbypassing the blade bearings and through the hub and again bypassing therotating part of the drive train by neutral brush(es) to the groundingsystem.

If the neutral brush(es) are not well connected or damaged, there is arisk the electrostatic energy (and lightning) will go through either themain shaft bearings and the small sparks will damage the bearing balls,or even worse will go through the gearbox or generator and damage thosemain components.

Monitoring the status of the neutral brush is possible usingmeasurements from two sensors which may be a voltage detector 130, orcurrent sensor, or any similar sensor for detection of passage ofcharges.

Thus, in the simplest ground diagnostic system 100 only two measurementsalong the grounding path are needed. However, due to general complexityof a wind turbine generator 12 the grounding diagnostic system may havemore sensors (current sensor/voltage detector or any similar) or sensornodes 45 to divide the diagnostic of the grounding path 122 into severalstretches or paths.

Thus, if sensor node 45X+1 measures a higher energy or voltage than thesensor node 45X there is an in-correct grounding path before sensor node45X.

FIG. 5 illustrates a wind turbine generator 12 with a grounding systemin a nacelle 19 — with grounding along a grounding path 122. The figureshould be seen in connection with FIG. 6 , which shows a situationwherein the grounding is along an incorrect grounding path 128.

The WTG 12 comprises blades 22 connected to the nacelle 19 via a rotor14. The blades 22 will function as a charge collecting structure 120 andwill experience lightning strikes 192 and electrostatic discharge 194.

The grounding system 100 comprises a grounding path 122 designed totransport the charge to the ground 190, such that sensitive equipment isprotected, e.g. bearings, WTG gearbox 30 or WTG generator 28.

In the present case, the nacelle 19 is equipped with two voltagedetectors 130I, 130II positioned at two different grounding path points124I, 124II.

The voltage detector 130I is positioned along the intended groundingpath 122.

The voltage detector 130II is positioned along an in-correct groundingpath 128.

Both voltage detectors 130I, 130II may be contactless voltage detectors.

Although voltage detectors are positioned at the nacelle 19, they can beused to determine whether one or more neutral brushes at the blades 22A,22B are damaged or otherwise works improperly. The neutral brushes areindicated by a grounding path critical transition 126A, 126B.

In this case, the neutral brushes work as intended, thus the voltagedetector 130I will measure the highest voltage during the dischargingand the voltage detector 130II will measure a small voltage or novoltage during the discharge. Thus, U(130I) > U(130II).

In this case the risk of damaging the bearings, WTG gearbox 30 or WTGgenerator 28 is minimized.

FIG. 6 illustrates a WTG 12 with a grounding system in a nacelle 19 withgrounding along an in-correct grounding path 128. The figure should beseen in connection with FIG. 5 , which shows a situation wherein thegrounding is along a correct grounding path 122.

The WTG 12 and grounding diagnostic system 100 is identical to the WTG12 of FIG. 5 .

In this case, one or more of the neutral brushes are defected and thegrounding does not follow the path over the critical groundingtransition 126A, 126B. The grounding then follows another path, which isan in-correct grounding path 128. The in-correct grounding path can bethrough the bearings, WTG gearbox 30 or WTG generator 28.

In this case, the voltage detector 130II will measure the highestvoltage during the discharging and the voltage detector 130I willmeasure a small or no voltage during the discharge. Thus, U(130II) >U(130I).

In this case, the risk of damaging the bearings, WTG gearbox 30 or WTGgenerator 28 is high, because the charge travels through the sensitiveequipment.

I.e if the neutral brush(es) are not well connected or damaged, there isa risk, the electrostatic energy (and lightning) will go through eitherthe main shaft bearings and the small sparks damaging the bearing balls,or even worse will go through the gearbox or generator and damage thosemain components.

FIG. 7 illustrates a configuration of a ground diagnosing system 100using an electrostatic motor 140 and with electrostatic energyharvesting.

Each power transmission 170 is disclosed by one or more arrows betweenthe different elements.

The electrostatic motor 140 is connected to a charge collectingstructure 120 of a not shown structure 1. The structure 1 may be any ofthe structures 1 shown in FIGS. 1-6 .

The electrostatic motor 140 is positioned along a grounding path 122 ofthe charge collecting structure 120 and is thus connected to the ground190.

The electrostatic motor 140 drives a shaft connected to a gearbox 160,which is connected to generator means 150 such as a generator 152,wherein the generator 152 generates electric power.

In some embodiments, the electrostatic motor 140 drives a shaft directlyconnected to a generator means 150 such as a generator 152, wherein thegenerator 152 generates electric power.

The generator means 150 or generator 152 is connected to a powermanagement circuit 154 which is connected to energy storage 156, such asa cell or battery or capacitor or super capacitor or any similar storagecomponents.

The energy storage 156 powers a sensor node 45.

The energy storage 156 may in addition power other power consuminginstallations. This is particularly useful in a rotor or blade whereinthere is otherwise limited power.

The sensor node 45 may monitor an output 142 from the electrostaticmotor 140; this can be a RPM measurement of the shaft for classificationof the charge collecting structure.

This can also be a torque measurement of the shaft for classification ofthe charge collecting structure.

A drop in the voltage would cause the RPM or the torques values tolower.

The sensor node 45 could likewise measure an output 142 of the gearbox160, the output 142 of the gearbox 160 could be the RPM or the torque ofa shaft of the gearbox 160.

The sensor node 45 could likewise measure an output 142 of the generatormeans 150 or generator 152 such as a voltage.

The sensor node 45 communicates by wire or wireless with a collectioncabinet 50 having a communication module 54, the collection cabinet 50being positioned in a structure 1 or nacelle 19.

Thereby, the ground diagnosing system 100 is able to monitor the qualityof the grounding connection from the structure 1 or the blades 22 whileutilizing static electricity for power generation.

The ground diagnosing system 100 will be able to:

-   perform quantization of lightning strikes 192-   estimate intensity of lightning strikes 192-   monitor static discharge — efficiency of grounding-   power generation and energy storage 156-   power sensor node 45 and other power consuming installations.

FIG. 8 illustrates a configuration of a direct ground diagnosing system100 using an electrostatic motor 140;

The electrostatic motor 140 is connected to a charge collectingstructure 120 of a not shown structure 1. The structure 1 may be any ofthe structures 1 shown in FIGS. 1-6 .

The electrostatic motor 140 is positioned along a grounding path 122 ofthe charge collecting structure 120 and is thus connected to the ground190.

The electrostatic motor 140 may drive a shaft.

The sensor node 45 may monitor an output 142 from the electrostaticmotor 140, this can be a RPM measurement of the shaft for classificationof the charge collecting structure.

This can also be a torque measurement of the shaft for classification ofthe charge collecting structure 120.

A drop in electrostatic charge would cause the rotational speed or thetorque’s values to lower.

The sensor node 45 communicates by wire or wireless with a collectioncabinet 50 having a communication module 54, the collection cabinet 50being positioned in a structure 1 or nacelle 19 or even outside thestructure at any given location.

FIG. 9 illustrates a configuration of direct grounding diagnostics 100using voltage detector 130. The voltage detector 130 is typicallypositioned near a grounding path 122 of the charge collecting structure120 to the ground 190.

The voltage detector 130 may be positioned on or near a criticalstructure such as bearings, where the voltage detector 130 should notmeasure a voltage and if the voltage detector 130 measures a voltage,this is due to an in-correct grounding path 128.

The voltage detector 130 can be a contactless voltage detector 130,which blinks periodically according to the voltage level.

The voltage detector 130 can be a detector called VKP-FF-35.

The voltage detector 130 has a light emitter, wherein the light blinkingperiod is correlated to the voltage level, which is a measurement of theefficiency of the grounding path.

However, the blinking period i.e. output signal of the voltage detector130 can be monitored by a sensor node and transfer a signal wirelessly(or by wire) to the data collection cabinet. Alternatively, a visualinspection camera may be used to monitor the blinking period.

The voltage detector 130 communicates by wire or wireless with acollection cabinet 50 having a communication module 54, the collectioncabinet 50 being positioned in a structure 1 or nacelle 19.

The voltage detector 130 setup may be implemented alone as disclosed. Itmay be optional in connection with an electrostatic motor setup.

FIG. 10 illustrates a configuration of grounding diagnostics usingvoltage and energy harvesting.

The configuration is similar to the configuration disclosed in FIG. 9 .However, instead of using the energy to make a light emitter blink, theenergy is stored and used for other purposes.

A voltage detector 130 may be in connection with a grounding path of thecharge collecting structure connected to the ground, or the voltagedetector 130 may be able to wireless detect the voltage

The voltage detector 130 can be a modified version of the detectorcalled VKP-FF-35.

The voltage detector 130 is connected to a power management circuit 154.

The power management circuit 154 is connected to energy storage 156.

The energy storage 156 may power other power consuming installations 180such as a System-on-a-Chip (SoC) which may contain one or more corecapabilities such as software, processor/microprocessor, networking,memory, data storage, processing etc. Alternatively any combination ofprocessing unit (microcontroller, microprocessor or any similar units)may be used for the installation. The energy storage 156 may power otherelectrical power consuming installations 180 located in the rotor, likefor example any electrical consuming electronics or motors, such as forexample blade pitch motors or blade de-icing systems.

The energy storage 156 is connected to a sensor node 45 in wired orwireless communication with a collection cabinet 50 having acommunication module 54. The collection cabinet 50 may be positioned inthe structure 1 or nacelle 19.

FIG. 11 illustrates a method of diagnosing 1000 a grounding system 100of a structure 1.

The method of diagnosing 1000 a grounding system 100 of a structure 1comprises a charge collecting structure 120 conductively connected tothe ground 190 via a grounding path 122. The diagnosing 1000 involves anact of monitoring 1100 an output 142 of an electrostatic motor 140connected to the grounding path 122.

The output 142 of the electrostatic motor 140 is a function of collectedcharge conducted to the ground 190; and wherein the output 142 is afunction of relative measures performed and chosen amongst:

-   a measure of rotational speed of the electrostatic motor;-   a measure of torque of the electrostatic motor;-   or combinations thereof;-   and relative to a respective calibrated measure performed.

The grounding system 100 may be a lightning protection system 102 andthe structure 1 comprises parts of a WTG 12.

Optionally, the method 1000 comprises a further act of generating 1200power by generator means 150 driven by the electrostatic motor 140 Thiscan performed as disclosed in FIG. 7 .

Thereby, the act of monitoring 1100 is powered by the power generated bythe generator means 150.

Optionally, the structure 1 comprises a blade 22 and wherein the act ofmonitoring 1100 further comprises acts of:

-   detecting 1300 a lightning strike 192;-   detecting 1300 electrostatic discharge 194;-   or combinations thereof.

Detection 1300 may also include detecting unstable, missing, or noelectrostatic discharge, which is the case when the grounding system ispartly or fully disconnected.

In another embodiment of diagnosing 1000, a grounding system 100 is of astructure 1 comprising a charge collecting structure 120 conductivelyconnected to the ground 190 via a grounding path 122.

Wherein diagnosing 1000 involves an act of monitoring 1100 output 142I,142II of a voltage detector 130I, 130II connected to the grounding path122.

The diagnosing 1000 may involve an act of comparing 1400 outputs 142I,142II of at least two voltage detectors 130I, 130II connected at twodifferent points 124I, 124II of the grounding path.

In a further embodiment, the method of diagnosing 1000 is performed as afunction of both of the previously described embodiments of the methodof diagnosing 1000.

EXAMPLE ITEMS

1. Method of diagnosing (1000) a grounding system (100) of a structure(1) comprising a charge collecting structure (120) conductivelyconnected to the ground (190) via a grounding path (122), whereindiagnosing (1000) involves an act of monitoring (1100) an output (142)of a rotating electrostatic motor (140) connected to the grounding path(122).

2. The method (1000) according to ITEM 1 wherein the output (142) of theelectrostatic motor (140) is a function of collected charge conducted tothe ground (190), and wherein the output (142) is a function of relativemeasures performed and chosen amongst:

-   a measure of rotational speed of the electrostatic motor (140);-   a measure of the torque of the electrostatic motor (140);-   or combinations thereof;-   and relative to a respective calibrated measure performed.

3. The method according to ITEM 1 or 2, comprising a further act of

-   generating (1200) power by generator means (150) driven by the    electrostatic motor (140).

4. The method according to ITEM 3, wherein the act of monitoring (1100)is powered by the power generated.

5. The method according to any of ITEMs 1 to 4, wherein the groundingsystem (100) is a lightning protection system (102) and the structure(1) comprises parts of a wind turbine generator (WTG).

6. The method according to ITEM 5, wherein the structure (1) comprises ablade (22) and wherein the act of monitoring (1100) further comprisesacts of

-   detecting (1300) a lightning strike (192)-   detecting (1300) electrostatic discharge (194)-   or combinations thereof.

7. Grounding diagnostic system (100) having an electrostatic motor (140)and computer implemented means adapted to execute the acts of one ormore of ITEMs 1 to 6.

8. The grounding diagnostic system (100) according to ITEM 7, whereinthe electrostatic motor (140) is configured with power generating means(150) to generate power.

9. The grounding diagnostic system (100) according to ITEM 8, furtherconfigured with the power generating means (150) powering the groundingdiagnostics system (100) alone.

10. A computer program product comprising instructions to cause thegrounding diagnostic system (100) according to ITEMs 7 to 9 to executethe act of the method ITEMs 1 to 6.

11. Method of diagnosing (1000) a grounding system (100) of a structure(1) comprising a charge collecting structure (120) conductivelyconnected to the ground (190) via a grounding path (122), whereindiagnosing (1000) involves an act of monitoring (1100) output (142I,142II) of a voltage and/or current and/or electrostatic detector(130I,130II) connected to the grounding path (122).

12. The method according to ITEM 11, wherein diagnosing (1000) involvesan act of comparing (1400) outputs (142I, 142II) of at least two voltagedetectors (130I,130II) connected at two different points (124I, 124II)of the grounding path (122).

13. Grounding diagnostic system (100) having at least two voltagedetectors (130I,130II) and means adapted to execute the acts of one ormore of ITEMs 11 to 12.

14. Method of diagnosing (1000) a grounding system (100) of a structure(1), wherein diagnosing (1000) is performed as a function of

-   diagnosing according to ITEMs 1 to 6; and-   diagnosing according to ITEMs 11 to 12.

15. Grounding diagnostic system (100) having an electrostatic motor(142) and means adapted to execute the acts of one or more of ITEMs 1 to6; having at least two voltage detectors (130I, 130II) and means adaptedto execute the acts of one or more of ITEMs 11 to 12; and having meansadapted to execute the acts of ITEM 14.

16. Use of a rotating electrostatic motor (140) arranged in a windturbine generator (WTG) to diagnosing (1000) an operational condition ofthe wind turbine generator (WGT).

17. The use according to ITEM 16, wherein the diagnosing (1000) is ofdegeneration in the wind turbine blades (22) of the wind turbinegenerator (WGT).

18. The use according to ITEM 17, wherein the diagnosing (1000) isperformed

-   by comparing a diagnostic output from a rotating electrostatic motor    (140) coupled to one blade (22A) with a diagnostic output from    another rotating electrostatic motor (140) coupled to another blade    (22B) on the same wind turbine generator (WTG),-   by comparing a diagnostic output from a rotating electrostatic motor    (140) coupled to one blade (22A) with a diagnostic output from a    another rotating electrostatic motor (140) coupled to a similar    blade (22B) of another wind turbine generator (WTG),-   by comparing a diagnostic output from a rotating electrostatic motor    (140) coupled to one blade (22) with a reference value, or-   combinations thereof.

19. The use according to ITEM 16, wherein the diagnosing (1000) is of agrounding system (100) of the wind turbine generator (WTG)

20. The use according to ITEM 16, wherein the diagnosing (1000) is of awind speed under which the wind turbine generator (WTG) is operating.

21. The use according to ITEM 16, wherein the diagnosing (1000) is of alightning strike of the wind turbine generator (WTG) and performed usinga rotating electrostatic motor (140).

22. The use according to ITEM 16, wherein the diagnosing (1000) isperformed discriminating between a lightning event and electric chargeaccumulation.

23. The use according to ITEM 21 or 22, wherein the diagnosing oflightning includes accessing characteristics of the output from therotational electrostatic generator at either the wave front, wave tail,or both.

1-23. (canceled)
 24. A method of diagnosing a grounding system of astructure comprising a charge collecting structure conductivelyconnected to the ground via a grounding path, wherein diagnosinginvolves an act of monitoring output of a voltage and/or current and/orelectrostatic detector connected to the grounding path.
 25. The methodaccording to claim 24, wherein diagnosing involves an act of comparingoutputs of at least two voltage detectors and/or current detectorsand/or electrostatic detector connected at two different points of thegrounding path.
 26. The method according to claim 25, wherein the atleast two voltage detectors and/or current detectors and/orelectrostatic detectors monitor the status of the neutral brush on astructure being a wind turbine generator.
 27. The method according toclaim 24, wherein the voltage detector and/or current detector and/orelectrostatic detector is positioned at the interface between a rotorand a nacelle; and/or at the interface between a tower and the nacelle;and/or at the interface between a blade and the hub.
 28. A groundingdiagnostic system comprising at least two voltage detectors and/or acurrent detector and/or an electrostatic detector, the groundingdiagnostic system being adapted to execute the method of claim
 24. 29. Amethod of determining grounding of a grounding system of a wind turbinegenerator, wherein the method comprises acts of building up electriccharge in a capacitor by collecting electrostatic charge from at leastone wind turbine blade.
 30. The method according to claim 29, whereinthe method comprises discharging the capacitor at a discharge chargelevel or discharge voltage at a point on the wind turbine blade;measuring a grounding charge level or grounding voltage at a groundingsystem point of the wind turbine; and determining grounding of thegrounding system as a function of the discharge charge level ordischarge voltage and the grounding charge level or grounding voltage.31. The method according to claim 30, wherein the grounding system pointbeing located in the nacelle, in the tower, or blade of the wind turbinegenerator (WTG).
 32. A wind turbine generator (WTG) comprising a tower,a nacelle, blades, sensor nodes and a grounding system along a groundingpath, wherein the sensor nodes are positioned along the grounding pathand along an incorrect grounding path; and wherein the sensor nodescomprise voltage detectors and/or current detectors and/or electrostaticdetectors.
 33. The wind turbine generator (WTG) according to claim 32,wherein sensitive equipment is not along the grounding path.
 34. Thewind turbine generator (WTG) according to claim 32, wherein a sensornode is placed at sensitive equipment such as bearing, or WTG gearbox orWTG generator along the incorrect grounding path.
 35. The wind turbinegenerator (WTG) according to claim 32, wherein the blades compriseneutral brushes at grounding path critical transitions and voltagevalues between sensors nodes along the grounding path and along anincorrect grounding path are compared.